Search now works with MapLibre's own geocoder control

@unmap/maps/geocoder puts unmap search behind MapLibre's own search control: install the plugin, add the control, and results come back in the shape the Mapbox geocoder already uses.

• createGeocoder builds @maplibre/maplibre-gl-geocoder, MapLibre's own search control, wired to the unmap gateway: add it to a map with map.addControl, no shadcn required.
• The plugin draws the input, the suggestion list, the fly-to, and the marker; unmap answers its searches.
• Results arrive as Mapbox-style Carmen features, so code written for the Mapbox geocoder reads them unchanged.